Confinement ring for use in a plasma processing system

ABSTRACT

An apparatus for confining plasma within a plasma processing chamber is provided. The plasma processing chamber includes a lower electrode for supporting a substrate and an upper electrode disposed over the lower electrode. The apparatus is a confinement ring that includes a lower horizontal section extending between an inner lower radius and an outer radius of the confinement ring. The lower horizontal section includes an extension section that bends vertically downward at the inner lower radius, and the lower horizontal section further includes a plurality of slots. The confinement ring further includes an upper horizontal section extending between an inner upper radius and the outer radius of the confinement ring and a vertical section that integrally connects the lower horizontal section with the upper horizontal section. The extension section of the lower horizontal section is configured to surround the lower electrode when installed in the plasma processing chamber.

PRIORITY CLAIM

This application is a Continuation of U.S. patent application Ser. No.15/669,742, filed on Aug. 4, 2017, entitled “CONFINEMENT RING FOR USE INA PLASMA PROCESSING SYSTEM”, which is a further continuation of U.S.patent application Ser. No. 12/872,984, filed on Aug. 31, 2010, (U.S.Pat. No. 9,779,916, issued on Oct. 3, 2017), entitled “RADIO FREQUENCY(RF) GROUND RETURN ARRANGEMENTS”, which claims priority to U.S.Provisional Patent Application No. 61/238,670, filed on Aug. 31, 2009,entitled “RADIO FREQUENCY (RF) GROUND RETURN ARRANGEMENTS,” which areherein incorporated by reference.

BACKGROUND

Advances in plasma processing have provided for growth in thesemiconductor industry. In today competitive market, a manufacturingcompany needs to be able to minimize waste and produce high qualitysemiconductor devices. During substrate processing, conditions of thechamber may impact substrate processing. A critical parameter that mayaffect the plasma processing of substrates is the flow of the radiofrequency (RF) current.

To facilitate discussion, FIG. 1 shows a simple block diagram of acapacitively-coupled plasma processing system with a processing chamber100. Consider the situation wherein, for example, a substrate 106 isbeing processed within processing chamber 100. To ignite the plasma foretching substrate 106, a gas may interact with an RF current. Thecurrent may flow from an RF supply 122 along a cable 124 through an RFmatch 120 into processing chamber 100 during substrate processing. TheRF current may travel along a path 140 to couple with the gas reactantto create plasma within a confined chamber volume 110 for processingsubstrate 106, which is positioned above a bottom electrode 104.

In order to control plasma formation and to protect the processingchamber walls, a set of confinement rings 112 may be employed. Set ofconfinement rings 112 may be made of a conductive material such assilicon, polysilicon, silicon carbide, boron carbide, ceramic, aluminum,and the like. Usually, set of confinement rings 112 may be configured tosurround the periphery of confined chamber volume 110 in which a plasmais to form. In addition to set of confinement rings 112, the peripheryof confined chamber volume 110 may also be defined by upper electrode102, bottom electrode 104, insulator rings 116 and 118, an edge ring 114and a lower electrode support structure 128.

In order to exhaust the neutral gas species from the confinement region(confined chamber volume 110), set of confinement rings 112 may includea plurality of slots (such as slots 126 a, 126 b, and 126 c). Theneutral gas species may traverse from confined chamber volume 110 intoan external region 132 (outside chamber volume) of processing chamber100 before being pumped out of processing chamber 100 via a turbo pump134.

Those skilled in the arts are aware that unconfined plasma may cause anunstable processing environment. Ideally, the plasma formed duringsubstrate processing is formed within confined chamber volume 110.However, under certain conditions, plasma may be ignited outside ofconfined chamber volume 110. In an example, given a high pressurizedenvironment, the neutral gas species (which are being exhausted fromconfined chamber volume 110 into external region 132 of processingchamber 100) may encounter an RF field/magnetic field. The existence ofRF current in the outside chamber may cause the formation of unconfinedplasma 150.

In a typical processing environment, the RF current flows from RFgenerator into confined chamber volume 110. Those skilled in the artsare aware that RF current flowing into processing chamber 100 usuallytries to return to its RF source. In a typical prior art configuration,a RF return path 142 may include the RF return current flowing along theinside of set of confinement rings 112. At point 152, the RF returncurrent may flow along the outside of confinement rings 112 to bridgewith the inside wall surface of processing chamber 100. From the chamberwall, the RF return current may follow a set of straps 130 to lowerelectrode support structure 128. From the surface of lower electrodesupport structure 128, the RF return current may flow back to RF source122 via RF match 120.

As can be seen from the foregoing, by following path 142, the RF currentflows outside of confined chamber volume 110 on its way back to RFsource 122. As a result, a magnetic field or a RF field may be generatedin the outside chamber region. The existence of an RF field/magneticfield may cause unconfined plasma 150 to be formed in external region132 of processing chamber 100.

Since RF return current tends to seek a low impedance path, a set ofstraps may be employed to provide a low impedance path, thereby creatinga shorter RF return path than path 142 (that follows the chamber wall),as shown in FIG. 2. In an example, a set of straps 230 may be employedto couple a confinement ring 212 to a lower electrode support structure228 within a processing chamber 200. Thus, when the RF return current(flowing along a path 242) flows along the bottom side of outer wall ofconfinement ring 212, the RF return current may encounter a set ofstraps 230. Since the set of straps 230 provide a lower impedance paththan the outer surface of confinement ring 212, the RF return currentmay bridge to lower electrode support structure 228 via set of straps230. From lower electrode support structure 228, the RF return currentmay continue onward to a RF source 222 via a RF match 220.

As can be appreciated from the foregoing, the RF return current path 242is significantly shorter than path 142 of FIG. 1. However, a magneticfield/RF field may be formed in a region 244 between set of straps 230and confinement ring 212. As a result, plasma may be ignited outside ofthe confined chamber volume (within region 244) given the rightcondition (such as the existence of gas reactants, a sufficiently highpressure volume, and an RF field/magnetic field).

Accordingly, an arrangement for providing a short RF return path whilepreventing the ignition of unconfined plasma is desirable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 shows a simple block diagram of a capacitively-coupled plasmaprocessing system with a processing chamber.

FIG. 2 shows a simple block diagram of a processing chamber with astrap-driven RF return path.

FIGS. 3A and 3B show, in embodiments of the invention, simple diagramsof a RF ground return arrangement.

FIGS. 4, 5, 6, and 7 show, in embodiments of the invention, RF groundreturn arrangements for an adjustable-gap processing chamber.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described in detail with reference toa few embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Various embodiments are described hereinbelow, including methods andtechniques. It should be kept in mind that the invention might alsocover articles of manufacture that includes a computer readable mediumon which computer-readable instructions for carrying out embodiments ofthe inventive technique are stored. The computer readable medium mayinclude, for example, semiconductor, magnetic, opto-magnetic, optical,or other forms of computer readable medium for storing computer readablecode. Further, the invention may also cover apparatuses for practicingembodiments of the invention. Such apparatus may include circuits,dedicated and/or programmable, to carry out tasks pertaining toembodiments of the invention. Examples of such apparatus include ageneral-purpose computer and/or a dedicated computing device whenappropriately programmed and may include a combination of acomputer/computing device and dedicated/programmable circuits adaptedfor the various tasks pertaining to embodiments of the invention.

In one embodiment, an apparatus for confining plasma within a plasmaprocessing chamber is provided. The plasma processing chamber includes alower electrode for supporting a substrate and an upper electrodedisposed over the lower electrode. The apparatus is a confinement ringthat includes a lower horizontal section extending between an innerlower radius and an outer radius of the confinement ring. The lowerhorizontal section includes an extension section that bends verticallydownward at the inner lower radius, and the lower horizontal sectionfurther includes a plurality of slots. The confinement ring furtherincludes an upper horizontal section extending between an inner upperradius and the outer radius of the confinement ring and a verticalsection that integrally connects the lower horizontal section with theupper horizontal section. The extension section of the lower horizontalsection is configured to surround the lower electrode when installed inthe plasma processing chamber.

In accordance with embodiments of the present invention, radio frequency(RF) ground return arrangements are provided. Embodiments of theinvention include establishing a short RF return path for the RF returncurrent by providing a direct RF contact (via a RF contact-enabledcomponent) between a confinement ring and a lower electrode supportstructure.

In this document, various implementations may be discussed using asingle confinement ring as an example. This invention, however, is notlimited to a single confinement ring and may be applied to a plasmaprocessing system with one or more confinement rings. Instead, thediscussions are meant as examples and the invention is not limited bythe examples presented.

In an embodiment of the invention, RF ground return arrangements areprovided for establishing a RF return path back to the RF source whilesubstantially eliminating the possibility of a magnetic field/RF fieldbeing established outside of the confinement region (region as definedby the periphery of the confinement ring). In an embodiment, the RFground return arrangements may be implemented within acapacitively-coupled plasma (CCP) processing system. The RF groundreturn arrangements may be implemented within a processing chamber witha fixed or movable lower electrode support structure, in an embodiment.

In one embodiment of the invention, a RF ground return arrangement maybe implemented with a RF gasket. The RF gasket may be made of aconductive material. In an embodiment, the RF gasket is in electricalcontact with the confinement ring and a lower electrode supportstructure (such as a ground ring).

For a processing chamber with a fixed lower electrode support structure,the RF gasket may be relatively small and may be either compliant ornon-compliant. However, in processing chamber with a movable lowerelectrode support structure, the RF gasket is configured to have a shapeand dimension to accommodate the movement of the ground ring as thelower electrode support structure is moved in a vertical direction. Inan embodiment, the shape of the RF gasket is configured to be a largecurvature design (for example, an upside-down or a sideway C-shapedflexible conductor RF gasket), thereby enabling the ground ring tomaintain RF contact with the confinement ring. In other words, the sizeof the RF gasket is at least equal to the size of the gap between thebottom-facing surface of the confinement ring and the upper-facingsurface of the ground ring. In addition, the RF gasket is compliant,thereby enabling the shape of the RF gasket to change as the ground ringmoves. In an example, as the ground ring moves upward (narrowing the gapbetween the ground ring and the confinement ring), the RF gasket isflattened. However, when the ground ring is at the furthest distancefrom the confinement ring, the RF gasket may have more of a half-donutshape.

In another embodiment, the RF ground return arrangement may beimplemented with a spring-loaded sliding contact arrangement. Thespring-loaded sliding contact arrangement may include a spring membercoupled to a confinement ring. The spring member is biased toward thewall of a ground ring. In an embodiment, the spring member is inelectrical contact with the wall of the ground ring via a contact point.Thus, as the ground ring moves up and down, the ground ring remains inRF contact with the confinement ring via the spring-loaded slidingcontact arrangement.

In yet another embodiment, the RF ground return arrangement may includea confinement ring with an extension. The extension may extend downwardand is parallel to a side wall of the ground ring. In an embodiment, theextension is positioned at a close proximity to the ground ring, therebynarrowing the gap between the extension and the ground ring. Theproximity of the extension to the ground ring creates a largecapacitance area. Since impedance is inversely proportional tocapacitance, the large capacitance area may create a low impedancereturn path for the RF return current.

Another RF ground arrangement, in an embodiment, may include a RFconductive rod in electrical contact with a confinement ring and aground ring. In an embodiment, the RF conductive rod is disposed withina conductive liquid, which resides within a recess area of the groundring. Thus, when the ground ring moves vertically, a part of the RFconductive rod remains in the conductive liquid of the ground ring. As aresult, RF contact is maintained between the confinement ring and theground ring via the RF conductive rod to provide a low impedance pathfor the RF return current.

As can be appreciated from the foregoing, the RF ground returnarrangements provide shorter RF return paths for the RF return currentin comparison to the prior art arrangements. In addition, each RF groundreturn arrangement does not encapsulate an area that is capable ofcreating an RF field/magnetic field and sustaining unconfined plasmaoutside of the confinement region.

The features and advantages of the present invention may be betterunderstood with reference to the figures and discussions that follow.

FIGS. 3A and 3B show, in embodiments of the invention, simple diagramsof one example of a RF ground return arrangement. Consider the situationwherein, for example, a substrate 306 is being processed within aprocessing chamber 300. In an embodiment, processing chamber 300 may bea capacitively-coupled plasma processing chamber. Substrate 306 may bepositioned above a bottom electrode 304. During substrate processing, aplasma 308, which may be employed to etch substrate 306, may be formedbetween substrate 306 and an upper electrode 302.

In order to control plasma formation and to protect the processingchamber walls, a set of confinement rings 312 may be employed. Set ofconfinement rings 312 may include a plurality of confinement rings ormay be one continuous ring. Set of confinement rings 312 may be made ofa conductive material such as silicon, polysilicon, silicon carbide,boron carbide, ceramic, aluminum, and the like.

Usually, set of confinement rings 312 may be configured to surround theperiphery of a confined chamber volume 310 in which plasma 308 is toform. In addition to set of confinement rings 312, the periphery ofconfined chamber volume 310 may also be defined by upper electrode 302,bottom electrode 304, insulator rings 316 and 318, an edge ring 314 anda lower electrode support structure 328.

During substrate processing, gas may flow from a gas distribution system(not shown) into confined chamber volume 310 and interact with RFcurrent to create plasma 308. RF current may be flowing from an RFsource 322 to an RF match 320 via a cable 324. From RF match 320, the RFcurrent may flow up along a path 340 through bottom electrode 304 tointeract with the gas within confined chamber volume 310 to form plasma308.

In order to exhaust the neutral gas species from the confinement region(confined chamber volume 310), set of confinement rings 312 may includea plurality of slots (such as slots 326 a, 326 b, and 326 c). The numberand size of slots on set of confinement rings 312 may vary dependingupon the rate of conductance required. The neutral gas species maytraverse from confined chamber volume 310 through the slots into anexternal region 332 (outside chamber volume) of processing chamber 300before being pumped out of processing chamber 300 via a turbo pump 334.

In the prior art, the existence of an RF field outside of theconfinement region may cause the RF current to interact with the gasreactant to ignite a plasma. Unlike the prior art, an RF ground returnarrangement is provided that substantially eliminates the generation ofplasma outside of confined chamber volume 310.

In an embodiment, a RF gasket 350 (see FIG. 3B) may be employed tocreate a RF contact between set of confinement rings 312 and lowerelectrode support structure 328 (such as a ground ring or anotherstructure electrically connected to RF source 322). RF gasket 350, in anembodiment is made from a conductive material, such as stainless steeland beryllium copper, for example. Although RF gasket 350 is shown witha circular design, RF gasket 350 may have other configurations, such asa half-donut shape, a square shape, a rectangular shape, and the like.As can be appreciated from the foregoing, the shape of the RF gasket mayvary based on manufacturer's preference as long as the RF gasketprovides the required RF contact between set of confinement rings 312and lower electrode support structure 328.

Unlike the prior art, RF gasket 350 creates a path 342 for the RF returncurrent without creating a region outside of confined chamber volume 310in which a magnetic field or a RF field may be formed. In other words,path 342 remains at the periphery of confined chamber volume 310 andeffectively creates a Faraday shield around the plasma, therebypreventing plasma unconfinement. Thus, the RF ground return arrangementprovides a short RF return path without encapsulating a region capableof sustaining plasma outside of confined chamber volume 310.

The RF ground return arrangement of FIGS. 3A and 3B may be implementedwithin a processing chamber with fixed lower electrode components. For aprocessing chamber that has movable lower electrode components, the RFground return arrangement may be implemented as shown in FIGS. 4, 5, 6,and 7.

FIG. 4 shows, in an embodiment of the invention, a RF ground returnarrangement for an adjustable-gap processing chamber 400. Similar toFIGS. 3A and 3B, a RF gasket 402 is employed to establish a RF contactbetween confinement ring 412 and a ground ring 428, which is part of amovable lower electrode support structure. In an embodiment, RF gasket402 is made of a flexible conductive material, such as stainless steel.In an embodiment, RF gasket 402 may have a half donut shape (such as theupside-down C-shape shown in FIG. 4, a sideway C-shape RF gasket, or anyother curved RF gasket design) that has a dimension large enough toprovide a large curvature area such that when the lower electrodesupport structure is moved vertically, ground ring 428 still remains inRF contact with confinement ring 412. Similar to RF gasket 350 of FIG.3, the shape of RF gasket 402 may vary based on manufacturer'spreference as long as RF contact is maintained between ground ring 428and confinement ring 412, thereby providing a short RF return path 442while confining plasma within the confined chamber volume.

FIG. 5 shows in an embodiment of the invention, a simple partial diagramof an adjustable-gap processing chamber 500 with a RF ground returnarrangement. In this configuration, the lower electrode supportstructure is movable. The lower electrode support structure may includea ground ring 528. Thus, as the lower electrode support structure movesup and down, ground ring 528 is also moving in the same direction.

In an embodiment ground ring 528 may include a recess 504 filled with aconductive liquid 506, such as mercury, for example. Disposed withinconductive liquid 506 is a RF conductive rod 508, which is made from aconductive material such as aluminum, for example. In an embodiment, RFconductive rod 508 is configured at least to couple a confinement ring512 to ground ring 528. In other words, a RF contact is establishedbetween confinement ring 512 and ground ring 528 via RF conductive rod508. To minimize the potential of exposing conductive liquid 506 to theconfined chamber volume, a gasket 510 (such as an o-ring) may beemployed.

Thus, as the confined chamber volume is adjusted by moving the lowerelectrode support structure vertically, a part of RF conductive rod 508continues to be disposed within conductive liquid 506, therebymaintaining the RF contact between confinement ring 512 and ground ring528. As a result, a RF return path 542 is provided for the RF returncurrent in which the path is significantly shorter than the prior artwhile substantially preventing a region to be established in the outsidechamber volume capable of sustaining a plasma.

FIG. 6 shows, in an embodiment of the invention, another RF groundreturn arrangement for an adjustable-gap processing chamber 600. Similarto FIGS. 4 and 5, the lower electrode support structure is movable andmay include a ground ring 602. Thus, as the lower electrode supportstructure moves vertically, ground ring 602 is also moving in the samedirection.

In an embodiment of the invention, the RF ground return arrangementincludes a spring-loaded sliding contact arrangement. In an embodiment,the spring-loaded sliding contact arrangement may be made from aconductive material, such as steel. The spring-loaded sliding contactarrangement may include a spring member 604. Spring member 604 may be aspring leaf, for example. Spring member 604 may be fixed to aconfinement ring 612 at a fixed point 606. In an embodiment, springmember 604 may include a contact point 608, which is biased against asurface 610 of ground ring 602.

Thus, as the lower electrode support structure is moving vertically,ground ring 602 also moves up and down while maintaining RF contact withconfinement ring 612. With the spring-loaded sliding contactarrangement, a short RF return path 642 is provided as the RF returncurrent traverses along the inside of confinement ring 612 to groundring 602 on its way back to the RF source.

FIG. 7 shows, in an embodiment, another RF ground return arrangement foran adjustable-gap processing chamber 700. In an embodiment, aconfinement ring 712 may include an extension 702. Extension 702 may beparallel to a side surface wall 704 of a ground ring 706, which is partof a movable lower electrode support structure.

Extension 702 is employed to create a large capacitance area betweenconfinement ring 712 and ground ring 706. Those skilled in the art areaware that the capacitance is inversely related to the impedance. Thus,the higher the capacitance value, the lower is the impedance value.

To create a high capacitance area (such as one with a capacitance of 10to 100 nanofarods, for example), extension 702 is positioned withinclose proximity to ground ring 706 since the capacitance of an area isdirectly proportional to the area and inversely proportional to thedistance between extension 702 and ground ring 706. With a highcapacitance, the gap (710) between extension 702 and ground 706 acts asa RF short and enables the RF return current to traverse fromconfinement ring 712 to ground ring 706. In other words, extension 702and ground ring 706 creates a low impedance path. Since the RF returncurrent tends to traverse the shortest path with the lowest impedance,the RF return path 742 as provided by extension 702 (via gap 710) ispreferable over path 142 of prior art FIG. 1. Thus, a shorter RF returnpath is provided while plasma is confined within the confinement chambervolume.

As can be appreciated from the forgoing, one or more embodiments of thepresent invention provide for RF ground ring arrangements configured forestablishing short RF return paths while substantially preventing an RFfield from being established in the outside chamber volume of theprocessing chamber. By creating RF return paths with relatively lowimpedance, the RF return current is more likely to traverse back to theRF source using the more desirable RF return paths as provided by the RFground return arrangements. With the RF return paths being kept awayfrom the external region of the processing chamber, the possibility ofigniting unconfined plasma outside of the confined chamber volume issubstantially eliminated.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. Although various examples areprovided herein, it is intended that these examples be illustrative andnot limiting with respect to the invention. In addition, even though theinvention is described in relation to a capacitively-coupled plasma(CCP) processing system, the invention may also be applied in relationto an inductively-coupled plasma processing system or a hybrid plasmaprocessing system.

Also, the title and summary are provided herein for convenience andshould not be used to construe the scope of the claims herein. Further,the abstract is written in a highly abbreviated form and is providedherein for convenience and thus should not be employed to construe orlimit the overall invention, which is expressed in the claims. If theterm “set” is employed herein, such term is intended to have itscommonly understood mathematical meaning to cover zero, one, or morethan one member. It should also be noted that there are many alternativeways of implementing the methods and apparatuses of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

What is claimed is:
 1. An apparatus for confining plasma within a plasmaprocessing chamber is provided, the plasma processing chamber includes alower electrode for supporting a substrate, a ground ring, and an upperelectrode disposed over the lower electrode, the apparatus comprising, aconfinement ring, including, a lower horizontal section extendingbetween an inner lower radius and an outer radius of the confinementring, the lower horizontal section includes an extension section thatbends vertically downward at the inner lower radius and is integral withthe lower horizontal section, and the lower horizontal section furtherincludes a plurality of slots; an upper horizontal section extendingbetween an inner upper radius and the outer radius of the confinementring, the inner upper radius of the upper horizontal section isconfigured to surround a portion of the upper electrode and the upperhorizontal section does not include slots and is positioned over theplurality of slots of the lower horizontal section; and a verticalsection disposed between the lower horizontal section and the upperhorizontal section, the vertical section having an outer surface thatextends to the outer radius; wherein the extension section of the lowerhorizontal section is configured to surround the ground ring that isdisposed around the lower electrode so that an inner facing surface ofthe extension section is positioned parallel and separated by a gap fromthe ground ring; wherein the gap provides for a capacitance between theextension section and the ground ring, and said capacitance provides forRF return currents to ground, when said confinement ring is installed inthe plasma processing chamber.
 2. The apparatus of claim 1, furthercomprising, an RF gasket, the RF gasket is disposed between theconfinement ring and the ground ring, the RF gasket provides conductionfor facilitating additional of said RF return currents to ground.
 3. Theapparatus of claim 1, wherein the lower horizontal section, the upperhorizontal section and the vertical section define a C-shaped structurethat is configured to confine plasma during processing by the plasmaprocessing chamber.
 4. The apparatus of claim 1, wherein the confinementring defined by the lower horizontal section, the upper horizontalsection and the vertical section is made from one of silicon, orpolysilicon, or silicon carbide, or boron carbide, or ceramic, oraluminum.
 5. The apparatus of claim 1, wherein the lower horizontalsection, the upper horizontal section and the vertical section form partof a confined chamber volume that is radially outside of a chambervolume defined between the lower electrode and upper electrode.
 6. Theapparatus of claim 1, wherein the extension section that bendsvertically downward at the inner lower radius of the lower horizontalsection is at a 90 degree angle relative to the lower horizontalsection.
 7. The apparatus of claim 1, wherein the extension sectionextends below a lower surface of the lower horizontal section.
 8. Theapparatus of claim 7, wherein each of the plurality of slots is disposedin the lower horizontal section in a region that is inside and betweenthe inner lower radius and the outer radius of the confinement ring. 9.The apparatus of claim 8, wherein each of the plurality of slots isconfigured to define a path for gases out of a confined volume formed bythe confinement ring, when the plasma processing chamber is inoperation.
 10. The apparatus of claim 1, wherein the vertical sectionseparates the lower horizontal section and the upper horizontal sectionby a separation distance that substantially a equal to a separationdistance between the lower electrode and upper electrode of the plasmaprocessing chamber, when the confinement structure is installed in theplasma processing chamber.
 11. The apparatus of claim 1, wherein anouter surface of the lower horizontal section, the vertical section andthe upper horizontal section define an exterior region relative to aconfined chamber volume that is facilitated by the confinement ring. 12.An apparatus for confining plasma within a plasma processing chamber isprovided, the plasma processing chamber includes a lower electrode, aground ring, and an upper electrode disposed over the lower electrode,the apparatus comprising, a confinement ring defined from a lowerhorizontal section, an upper horizontal section, a vertical section andan extension section, wherein the lower horizontal section extendsbetween an inner lower radius and an outer radius of the confinementring, the lower horizontal section includes an extension section that isoriented downward at the inner lower radius and is integral with thelower horizontal section, and the lower horizontal section furtherincludes a plurality of slots; the upper horizontal section extendingbetween an inner upper radius and the outer radius of the confinementring, the inner upper radius of the upper horizontal section isconfigured to surround a portion of the upper electrode and said upperhorizontal section does not include slots and is positioned over theplurality of slots of the lower horizontal section; and the verticalsection is disposed between the lower horizontal section with the upperhorizontal section, the vertical section having an outer surface thatextends to the outer radius; wherein the extension section of the lowerhorizontal section is configured to at least partially surround theground ring that is disposed around a region of the lower electrode sothat an inner facing surface of the extension section is positionedparallel and separated by a gap from the ground ring, wherein the gapprovides for a capacitance between the extension section and the groundring that enables RF return currents to ground from a plasma when struckin the plasma processing chamber.
 13. The apparatus of claim 12, whereina C-shape is formed by the confinement ring.
 14. The apparatus of claim12, wherein the confinement ring defined by the lower horizontalsection, the extension section, the upper horizontal section and thevertical section is made from one of silicon, or polysilicon, or siliconcarbide, or boron carbide, or ceramic, or aluminum.
 15. The apparatus ofclaim 12, further comprising, an RF gasket, the RF gasket is disposedbetween the confinement ring and the ground ring, the RF gasket providesconduction for facilitating additional of said RF return currents toground.
 16. The apparatus of claim 12, wherein the extension section isat a 90 degree angle relative to the lower horizontal section.
 17. Theapparatus of claim 12, wherein the extension section extends below alower surface of the lower horizontal section.
 18. The apparatus ofclaim 12, wherein each of the plurality of slots is disposed in thelower horizontal section in a region that is inside and between theinner lower radius and the outer radius of the confinement ring, andeach of the plurality of slots is configured to define a path for gasesout of a confined volume formed by the confinement ring, when the plasmaprocessing chamber is in operation.